Both polyrod and flared notch antennas are part of a larger family of antennas that exploit length in the endfire direction to achieve gain. A polyrod is a cylindrical shaped polystyrene rod a few wavelengths long. Other materials such as fiberglass may be used instead of polystyrene if desired. When properly excited, the polyrod acts as an endfire aerial. Traditionally, polyrods are fed with waveguide. A matching section is usually included to transition efficiently from the waveguide to the polyrod. As with other endfire antennas, like the flared notch, the gain of the polyrod may be increased by a corresponding increase in its length in the endfire direction, as described in The Antenna Engineering Handbook, H. Jasik, McGraw Hill, 1961, Chapter 16, pp. 16-1 to 16-24.
The waveguide required to feed the polyrod has proven incompatible with some of the proposed applications for the polyrod. One application, adding a polyrod array to the face of a mechanically scanned slot array, would be severely constrained if not impossible to accommodate using the waveguide. Not only would the waveguide feeding the polyrods be a problem because of the aperture blockage but also the feeding network for the waveguides would require more space.
Moreover, the waveguide is bulky and requires matching sections. Secondary to this is that the system, i.e., the polyrod and waveguide, is inherently narrow banded, i.e., limited at the low end by the cut-off frequency of the waveguide.
It would therefore be advantageous to provide a technique for feeding a polyrod antenna which has reduced volume and higher gain and broader operating bandwidth than the conventional waveguide-fed antenna.